We investigated the thermal stability of graphite oxides to heat treatment under ambient argon gas. Using X-ray diffraction, we observed the development of three phases in the annealed graphite oxides, instead of a mono-dispersed expanded interlayer distance as in the pristine graphite oxide. We found that the interlayer distances dropped off in a stepwise manner by approximately 0.1 nm in relation to the annealing time. The three phases are related to the stepwise decrease in the interlayer distances which is attributed to the removal of water molecules, hydrogen atoms from hydroxyl groups, and hydroxyl groups in the annealed graphite oxide. These changes were confirmed using Fourier-transformed infrared spectroscopy, thermogravimetric analysis, and elemental analysis. (C) 2009 Elsevier B. V. All rights reserved.